The key to popping a perfect manu lies in the bum. Before the body has even left the platform, or rock, or bridge, the bum is out. Arms up, back straight, knees bent, bum out. It’s known as the utkatasana (chair) pose in yoga and the “hurry up and jump” pose before a manu.

Once launched, the bum tucks in, making the body straight and tall as it gathers velocity on its way down to the water. When executed correctly, the body will fall fast and still. There’s a peaceful elegance to a manu before it’s been popped. Like someone meditating, or waiting for a lift to arrive.

The next move is to tuck. As the water draws nearer, the arms pull down and the legs swing up, folding the body in half as if stretching tight hamstrings.

The bum makes first contact with the water, a fleshy lantern held out by the rest of the body, saying here I am, let me in. As the lower back and the upper thighs follow, an executor of a perfect manu will already be extending, flinging limbs back and down, stretching out on the surface of the water. The shoulders and feet arrive last and fast, slapping the surface, forcing water around the body before it collapses into the cavity the bum has just created and explodes up into the air.

That’s a perfect manu, and exactly what Shelby Catley has just done at Lake Tikitapu in Rotorua on an overcast afternoon this summer.

It’s the qualifying round of the Bomb Comp, an annual national dive-bombing competition. Each of the more than 200 competitors has been given just one chance to impress the judges and be ushered through to the finals. The judges sit on lawn chairs, floating on a platform not unlike King Herod’s throne in Jesus Christ Superstar, and grade each bomber on their style, originality, splash volume, and splash height.

When Shelby steps out onto the eight metre platform, she doesn’t cut an imposing figure. She’s skinny, with shoulder blades and collarbones visible even from the ground. Among the competitors in the open grade, male and female, Shelby is comfortably the lightest. In a bomb comp, that’s not an advantage. She’s also light of skin, with an almost golden complexion and pale eyes, and stands out among the hundreds of people at the lake today. It’s hard to watch the national bomb comp and not notice that the overwhelming majority of competitors and spectators are brown.

No one can say for sure when the manu – or its variations – came into existence, let alone when they became a staple of New Zealand movement. Watch any YouTube clip with the words “manu” and “bomb” in the title and it’ll be accompanied by a heated debate in the comments over which town ‘invented’ the manu. Auckland bombers say it began in the early 1990s, with bomb competitions regularly held at the outdoor Moana-Nui-a-Kiwa pools in Māngere, while Raglan locals claim they’ve been popping manus since the old Kopua Bridge was built in 1963. Even the name has been brought into the dispute. Many call the act of entering the water bum first a manu, though some say ‘manu’ is merely an abbreviation of Māngere, its real name. Even then, Māngere could either be in reference to the pools or to the English translation of māngere being lazy, as in a lazy bomb. Tauranga locals call it a V-bomb, for obvious reasons.

Whatever the name, the manu may have been around long before anyone commenting on a YouTube video was born.

There are geysers everywhere in Whakarewarewa (The Living Māori Village), home of the Tūhourangi Ngāti Wāhiao people in the geothermal centre of Rotorua. There are geysers everywhere and one river running across the entrance to the village. In the early 1800s, the only way to visit the village was to be carried by the local men in exchange for a penny. When the first Whakarewarewa bridge was built in 1885, the custom of paying a penny to cross the river continued. Instead of being handed to the men, visitors – and now, tourists – would throw coins into the river and watch as the local children dived in to collect them.

It’s not a small drop into the river and the children soon learned to make a splash. According to folklore, if you could splash the tourists up on the bridge they were more likely to throw down extra coins. There’s no way to know whether the Māori kids of 150 years ago invented the manu technique, but the tradition of penny diving continues today and the manu is frequently employed.

Ten kilometres east of the penny divers, Shelby sits on the sand, adjusting her soaking wet basketball shorts. Shorts are the garment of choice for bombers, with not one pair of Speedos spotted all weekend. The shorts are a practical decision; popping a manu hurts a little when done well and hurts a lot when not. Any material helps to lessen the sting of impact so there’s always a smorgasbord at any bomb gathering: league shorts, sweat shorts, basketball shorts and, my personal favourite, jean shorts.

Shelby’s not just wearing shorts. “I wear two pairs of skins,” she says, pulling the waistbands out as proof. “Long skins then lycra then shorts on top. Just to try stop the slap as much as possible.” It’s a smart move, wearing tights, and she’s done it before. Shelby won the first ever Bomb Comp at Lake Taupō in 2016, popping manus in a full body wetsuit.

Her qualifying bomb was immaculate, but Shelby knows while technique is important, the bigger the body the bigger the splash. And the higher the jump, the higher the splash. Which means Shelby has to consider levelling up – to the highest platform, at 10 metres. “Even the eight metre I don’t usually do them off something that high. When I jumped off the 10 metre I was like,” she flails her arms around to demonstrate, “and it was scary so I dunno.”

As she’s speaking we watch a tiny figure walk out onto the five metre platform. He looks no older than two, is wearing board shorts, a life jacket, and a mullet. When he reaches the edge, he takes one look over the side to check that it’s clear, and ever so calmly, like taking that first step at the pedestrian crossing, walks off into the air. I’m laughing but no one else has given a second thought to the baby that just dropped five metres into a lake.

People like to call bombing a ‘Kiwi pastime’ even though it’s not. Backyard cricket is a Kiwi pastime. Eating sunken pavlova is a Kiwi pastime. Bombing is a Māori pastime, and to a lesser degree, a Pasifika pastime. Manus are free adventure. Getting a thrill costs money. Theme parks, sports matches, travel, even trampolines cost money. Spending all day at the river jumping off a rock is as free as the dirty water into which you’re jumping.

For Shelby, it was the Wairoa river and the Poripori waterhole. “I grew up around heaps of guys so we used to do reckless-as stuff, we went swimming in the river every day and I kinda just learned from there. I spent all holidays practically at the river.” It’s a common childhood story, including the reckless-as stuff. New Zealand’s most famous manu spot is the Ngaruawahia bridge. Stretching across the Waikato river at a guess of eight metres above the current, Ngaruawahia Bridge has become the place to be for manus and manu watching.

Spend half a summer’s day on the banks of the river there and be treated to every bomb technique in the book. The manu; the staple, which is entering hands and feet first, like a staple; the gorilla, almost an upside down-cannonball with the head and shoulders entering first in a forward motion; the leg pop is half a cannonball with one leg tucked and the other out; and the coffin, a feet first drop with a slight lean back to widen the splash area. They all have their strengths and weaknesses. The manu is the hardest technique to master, with a lot more movement throughout the fall. The coffin is the easiest, though none are easy to do well. While the skinny kids like Shelby can bend to the manu, the coffin is the style of choice for most larger bombers.

In the women’s bomb final at Lake Tikitapu, every competitor but Shelby is using the coffin technique because every competitor is at least twice her size. She’s at a severe disadvantage. One by one the older, larger women drop in perfectly weighted, water fleeing from them. Shelby knows she needs to do something extra. The height of the splash accounts for a massive 60 percent of the grade, but she can snatch an easy 10 percent with only the faintest style flare.

Arms up, back straight, knees bent, bum out. She launches, distancing herself from the eight metre platform and contorting into an outstretched star pose. Even deliberate, it looks as if she’s made a mistake and is flailing. A moment before impact she retracts her limbs and pops a near perfect manu. The crowd loves it. But even with a flawless technique and a touch of style, her splash is the same, if not lesser than, her competitors.

For her second and final attempt, Shelby ascends the extra steps to the 10 metre platform. It’s not something she wants to do but she’ll regret it if she doesn’t. She adjusts her shorts, glances habitually down to the empty landing area to check it’s clear, and jumps. There’s nothing fancy about it. It’s just a textbook manu. Her arms don’t flail as she feared they would but she overcorrects and lands flatter than expected. The splash is acceptable but nothing more.

A supporter is there, filming on her phone. Shelby watches the footage, still standing in the water, and shakes her head.

After the finals, the tower is opened up for anyone to jump. As the kids swarm the platforms, the announcer yells out instructions not to run and to “always swim out” of the landing area. They don’t need to be reminded, they’ve done this a thousand times. Though few have done it from a designated tower or platform.

In January 2017, the Waikato District Council banned bombing at every pool across the Waikato region. A child had been injured after another child landed on them at, of all places, Ngaruawahia pool, and that was the end of bombing in the very region where it was apparently birthed. Jumping into the pool is still allowed. A swimming dive is apparently still allowed. Manus are not allowed.

When a child died in 2002 after being struck by a train on the Ngaruawahia bridge, locals called for fencing to be put around the bridge to stop children from entering. But the children wanted to jump into the river and the bridge was the only platform for popping manus. So they climbed the fences and continued jumping. When bombing was banned at all Waikato pools, the bridge became one of the only spots for manus, with the extra-brave kids climbing the railings and jumping from a height of nearly 15 metres into the rushing current below. Last year, an 11 year-old was hit by a train on the bridge and died. Again, local adults called for extra preventative measures while the younger community asked for a purpose-built platform. We just want to have fun and swim, they said, why do you keep trying to stop us from doing that.

In researching this story I came across a news video showcasing young kids popping manus at the Auckland Viaduct. It looked like the perfect setup: the drop was only a few metres, there was a natural enclave as a landing area, and large terraced steps nearby made it easy for the swimmers to leave the water safely. The video was from December and showed a crowd of kids enjoying the area. On a hot, muggy Waitangi Day, I walked down to an empty viaduct. Auckland Council had installed a railing around the area, citing “health and safety concerns”.

The policing of young people’s hobbies is nothing new. Metal rods are scattered all over cities to prevent skateboarders from riding or grinding over public property. But at the same time, it’s not a long walk from anywhere in the country to a skate park. New Zealand has been systematically attempting to quash the one popular, free, and brown hobby this country has by restricting its use and providing no alternatives, forcing young children – who don’t have the luxury of paying for fun – to find it any way they can. Even if that means walking across a bridge and along train tracks to get there.

In Wellington, the council struggled for years to stop kids from jumping off a building into the harbour below. Ironically, the building was for the Wellington Free Ambulance. No threat of a fine or even arrest would curb the numbers. If the kids wanted to jump, they’d jump. So the council built a platform at the same location, specifically for manus. It’s packed out every sunny day while the ambulance building stands there, undisturbed.

On his way to the tower, a young Māori boy yells out to Shelby, “you had some awesome bombs!” She thanks him. “That last one from the very top hurt so much.” As he joins the line for the five metre platform, Shelby turns to the prizegiving happening onshore. The hundreds of kids on the tower don’t pause, even for a second, to find out who won. They genuinely don’t care. No one does, really.

Shelby isn’t confident. She thinks some of the larger, more experienced women had bigger splashes. We all know she had the best technique but sometimes that’s not enough. Whatever the result, she’s glad to have had a day out on the water, popping manus from way up.

“And the women’s open Bomb Comp champion is Shelby Catley!” The crowd cheers and whistles. They remember her from the first competition and, at only 16, she’s already a legend. She stands on the stage holding a comically large cheque for $1500, more than most professional female athletes get paid for a day’s work. Competitors from throughout the day mill around on the sand, their backs reddened from manus good and bad. The sound of frequent bombs continues from the lake as kids, teenagers, parents, and grandparents line up with equal enthusiasm to jump off a piece of metal and make a splash in the water.

When it gets dark, they’ll be asked to go home. Next weekend, they’ll go out to their local rivers and rocks and bridges, and stand there, ready to jump. Arms up, back straight, knees bent, bum out. Over and over again until it’s too dark to see the water below.